The invention relates to an electric injection molding machine. It relates especially to a transmission mechanism that transmits rotation of a motor to a screw shaft in the electric injection molding machine.
In an injection molding machine, resin heated and melted in a heating cylinder is injected into a cavity of a mold apparatus under high pressure so that the cavity is filled with the molten resin. The molten resin is then cooled and solidified so as to obtain a molded article.
The injection molding machine includes a mold clamping apparatus and an injection apparatus. The mold clamping apparatus is provided with a stationary platen, a movable platen and a mold clamping cylinder. The movable platen is advanced and retracted by the mold clamping cylinder, to thereby perform mold closing, mold clamping and mold opening.
The injection apparatus includes a heating cylinder for heating and melting resin supplied from a hopper, and an injection nozzle for injecting the molten resin. A screw is disposed inside the heating cylinder so that the screw can be rotated about an axis and can be advanced and retracted, i.e. moved rectilinearly along the axis of rotation. The screw is advanced so as to inject the molten resin, and retracted so as to meter the molten resin.
There has been provided an electric injection molding machine in which an electric motor is used to advance and retract the screw.
FIG. 1 is a schematic view of a conventional electric injection molding machine. In FIG. 1, a screw 101 is disposed inside a heating cylinder 100 so that the screw 101 can be rotated and can be advanced and retracted (i.e. moved leftward and rightward in FIG. 1). The rear end (rightward end in FIG. 1) of the screw 101 is fixed to a bearing box 109. At the rear (rightward in FIG. 1) of the heating cylinder 100, a drive section 102 is disposed for rotating, advancing and retracting the screw 101. The drive section 102 includes a frame 103, a metering motor 104 disposed movably forward and backward (leftward and rightward in FIG. 1) relative to the frame 103, and an injection motor 105 fixed to the frame 103.
A guide bar 106 is disposed on the frame 103 so that the guide bar 106 extends parallel with the screw 101. A support plate 107 is slidably disposed relative to the guide bar 106. The metering motor 104 is fixed to the support plate 107. Therefore, the metering motor 104 is moved forward and backward (leftward and rightward in FIG. 1) along the guide bar 106.
A drive-side pulley 108 is fixed to the output shaft of the metering motor 104. A driven-side pulley 110 is fixed around the outer surface of the bearing box 109. A timing belt 111 is extended between and wound around the drive-side pulley 108 and the driven-side pulley 110. The drive-side pulley 108, the driven-side pulley 110 and the timing belt 111 constitute the rotation transmission mechanism that connects the bearing box 109 and the metering motor 104.
In an injection stage, when the injection motor 105 is driven, the rotation of the injection motor 105 is transmitted to a ball screw shaft 112. Since a ball nut 113 is fixed to the frame 103, the ball screw shaft 112 is advanced while being rotated, so that the screw 101 is also advanced.
In this conventional injection molding machine, the metering motor 104, the support plate 107 and the bearing box 109 are moved by the advancing and retracting motion of the ball screw shaft 112. Therefore, mechanical vibration is increased in the injection stage since the mass of the moved portion is large. Meeting a predetermined injection speed is also delayed. Moreover, the reliability of electric wires to supply electricity to the metering motor 104 is deteriorated since the metering motor 104 is moved.
It is an object of the invention to provide an electric injection molding machine that can decrease mechanical vibration in the injection stage.
Another object of the invention is to provide an electric injection molding machine that can meet a predetermined injection speed rapidly.
A further object of the invention is to provide an electric injection molding machine that has the high reliability of electric wires to supply electricity to the metering motor.
To achieve the above object, an electric injection molding machine is provided and has a mechanical frame comprising a front plate and a rear plate, a heating cylinder fixed to the front plate, a screw disposed inside the heating cylinder so that the screw can be rotated about and can be advanced and retracted along an axis, a ball screw shaft which is disposed along the axis and which advances and retracts a screw shaft, a metering motor fixed to the front plate, and a rotation transmission mechanism which transmits rotation of the metering motor to the screw shaft. The rotation transmission mechanism is supported by the front plate and slidably engaged with the ball screw shaft along the axis.
The electric injection molding machine according to the invention further includes the heating cylinder fixed to a front portion of the front plate, the front plate having a cavity inside thereof, and the rotation transmission mechanism disposed inside the cavity.
The rotation transmission mechanism further includes a hollow shaft driven by the metering motor, a gear train which connects the hollow shaft to an output shaft of the metering motor, a screw support plate fixed to a rear end of the screw shaft, a bearing holder connected with the screw support plate and rotatably connected with a front end of the ball screw shaft, first spline cogs formed on an inner cylindrical surface of the hollow shaft, and second spline cogs formed on the bearing holder and slidably engaged with the first spline cogs along the axis.
Consequently, since the metering motor and the hollow shaft are not moved by the advancing and retracting motion of the ball screw shaft, the mass of the moved portion is small so that mechanical vibration is decreased in the injection stage. A predetermined injection speed is also met rapidly. Moreover, the reliability of electric wires to supply electricity to the metering motor is improved.
The above and further objects and novel features of the invention will more fully appear from the following detailed description when the same is read in connection with the accompanying drawings. It is to be expressly understood, however, that the drawings are for purpose of illustration only and are not intended as a definition of the limits of the invention.